The scale of human impacts

Free Power Secrets

Making Your Own Fuel

Get Instant Access

Our predecessors, even in hunter-gatherer times, had impacts on their environments. There are still debates about the extent to which early humans, as distinct from changing climate, contributed to the extinction of the Pleistocene megafauna in Europe, Africa, the Americas, and Australia, but there is no doubt that humans extinguished roughly half the bird species in Hawaii and New Zealand when they arrived less than 1000 years ago.

Significant though they were, these earlier impacts were not on the literally global scale of today's. It is estimated that humans now take to their own use, directly or indirectly, between 25 and 50% of all net terrestrial primary productivity (the commonly quoted figure is 40%; see Vitousek et al., 1986; Daily, 1997). Perhaps even more striking, it has been estimated that more than half of all the atoms of nitrogen, and also of phosphorous, incorporated into green plants today come from artificial fertilizers (produced with fossil-fuel energy subsidies) rather than the natural biogeo-chemical cycles which built, and which struggle to maintain, the biosphere. These estimates are necessarily imprecise, but they accord with a very recent study, using satellite imagery, which found 40% of the Earth's land surface being modified by human use, mainly for agriculture.

The Worldwide Fund for Nature (WWF, 2004) has presented estimates, country by country, of humanity's ecological footprint (EF) at current levels of consumption. The EF for a given country is defined as the biologically productive area required to produce the food and wood people consume, to give room for infrastructure, and to absorb the carbon dioxide emitted from burning fossil fuels. Thus estimated, the EF is expressed in 'area units'. Any such estimate is necessarily imprecise (the carbon dioxide bit arguably more so than other components), but on the other hand they are conservative in that other factors, such as requirements for natural ecosystem services to handle pollutants, are excluded. Having estimated individual countries' EF, the WWF adds them up to get the overall global EF shown in Figure 15.1. The observed increase over time derives partly from population growth, and partly from increases in the average footprint per person.

The WWF also estimate the total EF that individual countries, and thence the planet, could satisfy sustainably (the biological capacity, BC). Here the figures depend, to a degree, on assumptions about the footprints of future crops and energy sources. Figure 15.1 suggests we passed the point where humanity's actual EF exceeds the sustainable level—a milestone of milestones— around two decades ago. I again emphasize the ineluctable uncertainties in any such estimates

Figure 15.1 An estimate of the total ecological footprint of the human population, 1960-2001, as defined and discussed in the text. The straight line shows our planet's estimated biological capacity (BC)—the total ecological footprint available on a sustainable basis. The estimated actual total ecological footprint is expressed as a ratio to this baseline of 'one planet, used sustainably'. From WWF (2004).

Figure 15.1 An estimate of the total ecological footprint of the human population, 1960-2001, as defined and discussed in the text. The straight line shows our planet's estimated biological capacity (BC)—the total ecological footprint available on a sustainable basis. The estimated actual total ecological footprint is expressed as a ratio to this baseline of 'one planet, used sustainably'. From WWF (2004).

of footprints. Even so, I believe Figure 15.1 is indicative.

The most unambiguous sign that human activities now are on a scale that rivals natural processes is, of course, climate change. The evidence for this, including the statement from the Science Academies of all G8 countries along with China, India, and Brazil, was set out at the start of the previous chapter.

Was this article helpful?

0 0
Guide to Alternative Fuels

Guide to Alternative Fuels

Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.

Get My Free Ebook


Post a comment